The present invention relates to the in-flight refuelling of a squadron of aircraft and more precisely to the determination of the refuelling sequence best suited to the situation of the moment.
The current strategic context means that squadrons of aircraft are more and more often required to operate far from their base or for missions of relatively long duration requiring one or more in-flight refuelling operations. In-flight refuelling of a squadron of aircraft requires the organization of a rendezvous between the squadron of aircraft to be refuelled and the tanker and the determination of a refuelling sequence when the aircraft to be refuelled are more numerous than the refuelling hoses that the tanker has at its disposal.
For effective refuelling, an aircraft must approach very closely to the tanker, from the rear, enter its wake to the point of being exposed to its turbulence, grab a refuelling hose and remain attached thereto for the time required to transfer the desired amount of fuel, while continuing to be subjected to the turbulence of the tanker, which makes the flying tricky and means that refuelling taking place may be prematurely interrupted at any instant.
To determine a refuelling sequence, when the aircraft in a squadron have to be refuelled one after the other from the same refuelling hose, poses problems of the order of presentation of the aircraft to the refuelling hose and of the number of passes by each aircraft in the squadron to the refuelling hose in order to have the desired amount of fuel. These problems must be solved so as to optimize, at any instant, the in-flight refuelling operation, that is to say to ensure that the operational capacity of the squadron is maximized if the in-flight refuelling operation has to be prematurely interrupted for any reason and to minimize the number of passes by the aircraft to the refuelling hose, since each pass is an operation both tricky and expensive in terms of operating time.
The optimization, at any instant, of an operation for the in-flight refuelling of a squadron of aircraft, from the same refuelling hose, is accomplished, as a general rule, by organizing a queue ordered according to decreasing needs for fuel. A squadron of aircraft consists in fact, as a general rule, of aircraft of similar characteristics having fuel reserves and consumptions of the same order so that the endurances of the one or more aircraft of which the squadron is composed are, for most of the time, inversely proportional to their fuel demands.
It is preferable to refuel an aircraft in a single pass to the refuelling hose, but this is not always possible as the endurances of the other aircraft in the squadron have to be taken into account. This is because, for better efficiency of the in-flight refuelling of a squadron of aircraft, there is an advantage in providing the point of rendezvous of the squadron of aircraft with the tanker as late as possible, endeavoring to approach, without starting, the fuel reserves of the aircraft to be refuelled, which reserves must allow them, in all circumstances, to reach a rerouting airfield under acceptable safety conditions. However, it may happen, depending on the operational conditions, that the in-flight refuelling rendezvous is later than planned and that some of the aircraft in the squadron can no longer wait, in order to be refuelled, for the time needed for refuelling, in a single pass, the one or more aircraft that precede them in the refuelling queue. There are therefore two solutions, namely either to reroute the aircraft that can no longer wait to a rerouting airfield without effecting their in-flight refuelling, but the squadron is disorganized and its mission often compromised, or to shorten the refuelling of the aircraft preceding an aircraft that cannot wait its turn in order to try to be able to be refuelled in time before starting its fuel reserve. Provided that the one or more aircraft whose refuelling has been shortened have received a sufficient amount of fuel in order to allow them to wait, their refuelling may be completed by a further pass to the refuelling hose by being moved to the end of the queue.
For an in-flight refuelling of a squadron of aircraft from the same refuelling hose of a tanker, it is therefore necessary to provide, in addition to the point of rendezvous with the tanker, the order of the aircraft to be refuelled in the refuelling queue, the number of passes by the aircraft to the refuelling hose, preferably one but possibly two passes, and the amounts of fuel delivered at the various passes. This leads to a large number of possibilities for the in-flight refuelling of a squadron, most particularly when it contains three or four aircraft.
Currently, the organization of the in-flight refuelling of a squadron of aircraft is the responsibility of a refuelling controller on board the tanker, who decides the execution of a refuelling operation, the order of the aircraft to be refuelled in the refuelling queue, the number of passes to the refuelling hose and the amounts of fuel delivered at each pass, depending on the desiderata of the squadron leader and his personal experience. He has the greatest difficulty in finding the most optimum solution for continuing the squadron""s mission, each time that the deadlines are stretched relative to the fuel reserves of one or more aircraft in the squadron. In addition, this results, for a refuelled pilot and also for the squadron leader, in the need to take on, during a refuelling phase, a monitoring and planning task in addition to an already tricky flying operation.
It is therefore important to facilitate the organization of the in-flight refuelling of a squadron of aircraft whether this is on a mission over an area or is conveying.
The subject of the present invention is a method of managing the in-flight refuelling of a squadron of aircraft which can be automated, that is to say is capable of being operated by a computer, and which makes it possible to propose an optimum refuelling sequence, if one exists, that minimizes the number of passes, that is to say the number of operations to catch hold of the refuelling hose of the tanker, both from the overall standpoint of the squadron and from the standpoint of each of the aircraft of which it is composed, while providing the aircraft in the squadron, at the end of the refuelling operation, with the amounts of fuel required, on the basis of knowing the refuelling rendezvous point, the number of aircraft in the squadron, the amounts of fuel desired by the aircraft in the squadron at the end of refuelling, and the distances, from the refuelling rendezvous point, along the route followed by the tanker, of the limiting points that can be reached by the various aircraft in the squadron without refuelling and without them drawing on their fuel reserves.
The subject of the invention is also a method of management of the aforementioned type, making it possible to generate a refuelling sequence such that, during its execution, the operational capacity of the squadron is at the highest possible level throughout the refuelling operations.
The subject of the invention is a method of managing the in-flight refuelling of a squadron of n aircraft A1, . . . , An from the same refuelling hose of a tanker, making it possible to generate a refuelling sequence on the basis of taking into account a refuelling rendezvous point P, the number n of aircraft in the squadron, the amounts of fuel Q1, . . . , Qn demanded by the aircraft A1, . . . , An in the squadron at the end of refuelling and the maximum distances L1, . . . , Ln that can be covered by each aircraft in the squadron in waiting for the start of refuelling, these maximum distances L1, . . . , Ln corresponding to the distances separating the refuelling rendezvous point P, over the route followed by the tanker, from the limiting points that can be reached by the various aircraft in the squadron without refuelling and without them drawing on their fuel reserves. This method is noteworthy in that it comprises the following steps:
of initially taking an arbitrary refuelling sequence defined by the queuing of the aircraft in the squadron in an arbitrary order A1, . . . , An and a single pass by each aircraft in the squadron to the refuelling hose;
of testing the viability of the refuelling sequence adopted, consisting in expressing, as distances D1, . . . , Dn to be flown by the tanker, the times needed to deliver to the aircraft in the squadron the planned amounts of fuel during their passes to the refuelling hose and in verifying, by going down the queue, that each aircraft An, . . . , A1 will start its refuelling within the deadlines, that is to say before the tanker has flown a distance greater than the maximum distance Ln, . . . , L1 that can be covered by the aircraft in question;
when there is no finding that an aircraft will start its refuelling beyond the deadline, of accepting the viability of the refuelling sequence tested and of adopting it;
when there is a finding that an aircraft will start its refuelling beyond the deadline, of modifying the refuelling sequence tested in order to shorten the waiting time by this aircraft and of trying to fuel it within the deadlines, the modification in the sequence consisting in dividing, into two passes, the refuelling operation or operations of one or more aircraft that precede the aircraft in question in the queue, a first shortened pass to the refuelling hose allowing an aircraft to receive a minimum amount of fuel, increasing its endurance sufficiently for it to be able to move to the end of the queue and to wait for a second pass to the refuelling hose without drawing on its fuel reserve, the aircraft whose refuelling is divided into two being chosen so as to minimize the number of passes to the refuelling hose, the choice firstly depending on the aircraft, if there is one, that is placed ahead in the queue and the dividing of the refuelling of which into two passes to the refuelling hose makes it possible to approach as best as possible, by an upper value, the desired time saving, and then on the two aircraft, if they exist, placed ahead in the queue, the divisions of the refuelling of which make it possible to approach as best as possible, by an upper value, the desired time saving, and so on, the absence of a solution in the choice of the aircraft for divided refuelling resulting in a finding that it is impossible to refuel the entire squadron, whereas the presence of a solution leads to a modified refuelling sequence proposal; and
of taking any modified refuelling sequence proposal and testing its viability by restarting at the second step of the method.
Advantageously, should the viability test of the arbitrary refuelling sequence initially adopted be negative, this sequence is replaced with a refuelling sequence referred to as a nominal refuelling sequence defined by putting the aircraft in the squadron into a queue in an order corresponding to decreasing amounts of fuel demanded and by a single pass of each aircraft in the squadron to the refuelling hose, the first aircraft in the queue being that requiring the largest amount of fuel.
Advantageously, should the viability test of the arbitrary refuelling sequence initially adopted be negative, this sequence is replaced with a refuelling sequence defined by putting the aircraft in the squadron in a queue in an order corresponding to increasing maximum distances L1, L2, . . . , Ln that can be covered, the first aircraft in the squadron being the one that is able to cover the shortest maximum distance.
Advantageously, should a viability test of a refuelling sequence be negative owing to the finding that one aircraft in the squadron will start its refuelling beyond the deadline, the choice of the one or more aircraft, placed ahead in the queue, the refuelling of which is divided, results from systematic virtual tests carried out by going up the queue taking into consideration one aircraft, then two aircraft, including that one giving the greatest time saving, then three aircraft, including the two providing the greatest time saving, and so on.
Advantageously, the duration of the first shortened pass to the refuelling hose of a divided refuelling operation is set to the same value DMIN for all the aircraft in the squadron, which duration is progressively increased, once the refuelling sequence in question has satisfied the viability test, until reaching the endurance limit for one of the aircraft in the squadron.
Advantageously, the choice of the aircraft in the squadron whose refuelling is divided results from checking that a succession of inequality relationships between the flight distances D1, . . . , Dn needed by the tanker, in order to deliver the required amounts of fuel during each pass of the aircraft in the squadron to the refuelling hose and the maximum distances that can be covered by each aircraft in the squadron, is met.